The invention relates to the chronic elevation of endogenous adenosine levels by the use of stable adenosine 5xe2x80x2-triphosphate (ATP) compositions, which are taken orally over a period of time. The elevated levels of adenosine, produced by the in vivo degradation of ATP, act in decreasing the sensitivity (desensitization) of adenosine receptors. The decrease in sensitivity can materialize through a decrease in numbers of receptors (density) or through a reduction in the receptor""s coupling activity (intracellular signal transduction). The reduced sensitivity of certain adenosine receptors towards their natural agonistxe2x80x94adenosine, can be useful by itself or in combination with adenosine antagonists, which are much more active towards desensitized adenosine receptors. Examples for utilization of these methods are in the treatment of disorders or diseases, which are controlled by biochemical mechanisms regulated by adenosine receptors. One such case is in the treatment of obesity, which can be treated by the metabolic stimulation of weight loss. Lipolysis, the degradation of fat (triglycerides) in adipose tissue to free fatty acids and glycerol, is known to be inhibited by the interaction of adenosine with A1 adenosine receptors of the adipocyte (fat cell). The interaction of adenosine with adipose tissue A1 adenosine receptors was shown to stimulate lipogenesisxe2x80x94the buildup of triglycerides (fat) in fat cells. Methods for desensitization of A1 adenosine receptors in a human in vivo, thus significantly diminishing the activity of endogenous adenosine, are disclosed and taught and are utilized for the effective reduction of weight in humans. Effective weigh loss in humans can be achieved either by the desensitization of the adipose tissue adenosine A1 receptors by themselves, or by desensitization in combination with adenosine antagonists such as caffeine or theophylline, which are much more effective in blocking the action of adenosine once its receptors became desensitized. The use of chronic administration of adenosine for the purpose of desensitization of adipose tissue A1 adenosine receptors in the induction of weight loss in humans, demonstrates the utility of the present invention. Obesity is the costliest disease in industrialized countries. It is associated with a variety of chronic life-threatening diseases such as type II diabetes, hypertension, stroke, and heart disease. The definition of obesity is an excessive accumulation of fat in the body. Obesity in terms of a disease is defined if body weight is 20% or more above the desirable weight (Council on Scientific Affairs, J. Amer. Med. Assoc. 1988). Overweight is defined if body weight exceeds the desirable weight by less than 20%. Desirable weight in humans has been well-defined (council on scientific affairs, JAMA 1988). Weight loss in overweight or obese humans can be achieved by diet, physical activity and behavior modification or by treatment with drugs. There are three main ways for the pharmaceutical treatment of overweight or obesity: 1. Inhibition of absorption of nutrients in the intestine; 2. Modulation of the activities of the metabolic and central nervous system (hypothalamic) satiety and food consumption (hunger) signals; and 3. Induction of energy dissipation in tissues, especially adipose tissue (thermogenesis). The methods disclosed here of the chronic administration of adenosine by the oral delivery of the pro-drug ATP, deal with the induction of energy dissipation, in the form of degradation of fats in adipose tissue.
The physiological activities of adenosine triphosphate and adenosine were first discovered in 1929 (for a review, see Williams and Bumstock 1997). It is now known that adenosine exerts its physiological effects by interacting with specific receptors, several subtypes of which (A1, A2A, A2B and A3) have been characterized and shown to regulate specific physiological processes. Adenosine triphosphate in turn, exerts its physiological activities by interacting with another family of receptors termed P2 receptors (Bumstock 1990). The A1 adenosine receptors were shown to regulate significant brain (Williams and Bumstock 1997); heart and adipose tissue functions (van der Graaf et al. 1999) by their in vivo interactions with endogenous, extracellular adenosine in animals and humans. The function of these A1 adenosine receptors is to transmit regulatory signals from adenosine, which is the product of extracellular metabolism, to the inside of the cells. This signal transduction is in turn achieved by a family of G proteins-linked to cell membrane A1 adenosine receptors (Linden 1991). The Gi protein, which interacts with the A1 adenosine receptors, acts in inhibiting the intracellular activity of adenyl cyclase, the enzyme catalyzing the synthesis of cyclic AMP (cAMP) inside the cell. Thus, upon interaction of extracellular adenosine with A1 adenosine receptors, the Gi proteins coupled to this receptor inhibit the synthesis of cAMP, resulting in lower cellular levels of cAMP and in the case of adipose A1 adenosine receptors, overall inhibition of lipolysis (LaNoue and Martin 1994). Because signaling from the adipose tissue A1 adenosine receptors inhibit the degradation of triglycerides to free fatty acids and glycerol (lipolysis), the possibility of excessive activity of the adipose tissue A1 adenosine receptors was considered as a genetic factor in obesity. This indeed turned out to be the case in genetically obese mice and rats as well as in humans. In these cases the adipose tissue A1 adenosine receptors were found to be extremely active in transmitting their signal to the Gi proteins with little dependence on the presence of extracellular adenosine (LaNoue and Martin 1994).
Therefore, the inhibition of the activity of adipose tissue A1 adenosine receptors via antagonism of adenosine or a mediated reduction of the efficacy of the receptors""coupling to Gi proteins would constitute a reasonable approach to weight control or obesity in humans. Methods utilizing the administration of A1 adenosine receptor antagonists, such as caffeine (1,3,7-trimethylxanthine), theophylline (1,3-dimethylxanthine) or synthetic A1 adenosine receptor antagonists, did not produce weight loss in genetically obese experimental animals (Xu et al. 1998). However, Caffeine, which is an established non-specific A1 adenosine receptor antagonist (Jacobson and van Rhee 1997), was shown effective in inducing weight loss in humans as part of a variety of regimens discussed in several issued U.S. patents.
U.S. Pat. No. 5,422,352 discloses a combination of caffeine and ephedrine in a ratio of about 12:1 as a composition for reducing weight in humans. U.S. Pat. No. 5,480,657 discloses a composition of caffeine, chromium and fructose for the treatment of obesity. U.S. Pat. No. 5,679,358 discloses compositions containing caffeine, theophylline or their derivatives along with other ingredients for the purpose of reduction of superfluous fat of any origin by topical application. For example, this patent refers to caffeine, theophylline or pentoxifylline as lipolytic agents, though no mechanism is discussed in the specifications. U.S. Pat. No. 5,798,101 discloses compositions and methods for reducing weight consisting of St. John""s Wart herbal extracts with or without caffeine. Caffeine and theophilline have been established as non-specific antagonists of adenosine receptors, namely, they interact with both A1 and A2A adenosine receptors with moderate affinity (Jacobson and van Rhee 1997). All of the issued U.S. Patents discussed above refer to caffeine as a xe2x80x9cstimulator of metabolismxe2x80x9d or in one case a xe2x80x9clipolytic agentxe2x80x9d.
A published placebo-controlled double blind human clinical study has demonstrated that caffeine ingestion increased the levels of free fatty acids (the products of lipolysis) in young men in a statistically significant manner. The increase in free fatty acids after caffeine challenge was not related to alterations in norepinephrine kinetics or fat oxidation (Arciero et al. 1995).
Several physiological sites are regulated to a significant degree by A1 adenosine receptors. These are the brain (Williams and Bumstock 1997), the heart (Kollias-Baker et al. 1995), adipose tissue (van der Graaf et al. 1999) and the coordination of glucose and lipid metabolism (van Schaick et al. 1998). Attempts to affect the function of specific organs or tissues by the use of adenosine or synthetic adenosine analogues acting as agonists or antagonists would seemingly produce global effects leading to intolerable side effects. This is not the case however, because of the blood brain barrier, which protects the brain from hydrophilic agents and the much greater sensitivity of adipocytes-metabolic A1 adenosine receptors towards adenosine and its agonists in comparison to the heart A1 adenosine receptors. The overall sensitivity of adipose tissue anti-lipolytic A1 adenosine receptors towards adenosine, considering both the tissue density of the receptors and the sensitivity of the receptors""intracellular coupling, was reported to be 38 times higher than the sensitivity of A1 adenosine receptors regulating cardiac functions (van der Graaf et al. 1999). Adipose tissue-metabolic A1 adenosine receptors are therefore a good therapeutic target, taking into account their sensitivity towards adenosine in comparison to other potential therapeutic targets, which is expected to yield significant efficacy with a manageable spectrum of side effects. One condition is that the agonist for the adipose tissue-metabolic A1 adenosine receptors has to be a relatively low affinity agonist, since a high affinity agonist is expected to interact with low affinity A1 adenosine receptors on other organs and produce significant side effects (van der Graaf et al. 1999). Adenosine itself is known to be such an agonist (Jacobson and van Rhee 1997). The reason that it has not been used for these therapeutic targets is its extremely short blood plasma half-life, limiting any efficacy and potential usefulness (Williams and Burnstock 1997). The present invention discloses and teaches a method for consistently and chronically elevating blood plasma adenosine levels for achieving adipose tissue-metabolic therapeutic targets without any side-effects.
The short blood plasma half-life of adenosine of 3-6 seconds (Williams and Burnstock 1997) made it an ideal compound for the treatment of supraventricular tachycardia, a form of cardiac arrhythmia, for which use it has been approved in man as a bolus injection (Kollias-Baker et al. 1995). The therapeutic use of adenosine in the form of a bolus injection has been successful strictly because of the acute nature of the adenosine administration, preventing what is defined as receptor desensitization (Linden 1997). Chronic administration of synthetic A1 adenosine receptor agonists was reported to produce marked desensitization of the heart""s adenosine A1 receptors (Shryock et al. 1989; Lee et al. 1993)
Desensitization of receptors is a general phenomenon, whereby chronic exposure of sensitive receptors to their agonists can produce a marked reduction in the capacity of the receptors to respond to the same or related agonists. The same phenomena have also been termed refractoriness, tolerance or tachyphylaxis (Hoppe and Lohse 1995). The A1 adenosine receptors, both in cardiac and adipose tissues have been demonstrated to undergo desensitization after chronic exposure to adenosine analogues that are proven agonists for the A1 adenosine receptors. Desensitization of the A1 adenosine receptors in both tissues was demonstrated to be mediated by both a reduction in receptor density (numbers) and a decrease in the sensitivity of the receptor""s coupling to the intracellular Gi proteins (Hoppe and Lohse 1995). The Gi proteins act in transducing the receptors"" signal inside the target cell. The A1 adenosine receptors desensitization is used as a therapeutic target as disclosed and taught by the present invention. By reducing the overall sensitivity of the adipose tissue-metabolic A1 adenosine receptors as a result of chronic administration of adenosine, the effectiveness of adenosine as an endogenous anti-lipolytic agent is significantly diminished. As importantly, antagonism of adenosine at these sites, by common A1 adenosine receptor antagonists such as caffeine or theophylline, is markedly enhanced. Desensitization of adipose tissue-metabolic A1 adenosine receptors does not affect heart or brain A1 adenosine receptors because of the heart""s receptors much lower sensitivity (van der Graaf 1999) and the brain""s effective barrier against systemic adenosine (Williams and Burnstock 1997).
The present invention discloses and teaches:
The preparation of a stable pharmaceutical and therapeutic composition of adenosine 5xe2x80x2-triphosphate (ATP) or physiologically acceptable salt thereof suitable for oral delivery. The invention provides for a stable oral dosage form such as a pill of ATP or physiologically acceptable salt thereof along with fillers, binders, stabilizers and enteric coating materials. The objective of the oral delivery of ATP is to achieve systemic absorption of adenosine.
A method for the chronic administration of adenosine using an ATP oral dosage form (e.g. pill) as a pro-drug for the chronic elevation of extracellular adenosine. Extracellular adenosine interacts with a variety of adenosine receptors regulating functions of organs and tissues.
A method for the chronic administration of adenosine for the purpose of desensitizing adipose tissue-metabolic A1 adenosine receptors. The utility of this method is in decreasing the sensitivities of these receptors towards adenosine and at the same time increasing the sensitivities of these receptors towards adenosine antagonists such as caffeine or theophilline. This method is used for the purpose of inducing weight loss in humans or in the treatment of obesity in humans. Since the adipose tissue-metabolic A1 adenosine receptors act in inhibiting lipolysis (degradation of fats), reductions in their activities as a result of chronic exposure to adenosine is suffecient to induce lipolysis and effective weight loss. Chronic exposure to adenosine, can be supplemented by caffeine or theophilline, both commonly used drugs in order to further reduce the activities of adipose tissue-metabolic A1 adenosine receptors, thus achieving a more enhanced weight loss. The term xe2x80x9cchronic administrationxe2x80x9d and similar terms used herein refer to prolonged or substantially sustained release over an extended period of time, typically at least about 96 hours.
Pharmacologically active substances, such as ATP, which undergo rapid degradation inside parts of the gastrointestinal tract or inside the vascular bed, are coated with an enteric polymer that dissolves at a specific pH. In the case of ATP, the catabolic enzymes that catalyze the degradation of purines are present in the stomach and the proximal small intestines (Mohamedali et al. 1993). Thus a pH-sensitive enteric coating can be designed to release ATP as the therapeutically active agent in the distal part of the small intestine, the ileum, where catabolic activities that catalyze the degradation of ATP are minimal (Mohamedi et al. 1993). The human stomach has a variable acidic pH of about 1 to 2 and the transit time of a pill through the stomach is between 20 minutes and 2 hours, depending on the prandial state. An ATP pill passing through the stomach intact would enter the small intestine, which consists of the duodenum, jejunum and ileum. Transit time of a pill throughout the small intestine is relatively steady at approximately 3 hours. Following the small intestine, an enteric stable pill then passes through the large intestine, which consists of the caceum, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. Total transit time through the large intestine is about 30-35 hours. Even though the distal part of the small intestine, the ileum, has somewhat greater catabolic activities on ATP than the colon, three of its properties make areas of the ileum very suitable sites for the release of ATP from enteric pills. First, a pH spectrum that enables the design of a pH-sensitive enteric coated pill, releasing the ATP at the desired site. The pH of the small intestine gradually rises from about 5-5.5 in the duodenal bulb, the site of gastric emptying, to about 7.2 in the distal parts of the ileum. The pH then drops at the ileum-caceum junction to about 6.3 and gradually increases to about 7 in the descending (left) colon. Second, absorption of purines from the small intestine is fast, providing for minimal degradation after release of the therapeutically active substance and a predictable delivery of specific dosage forms. Third, residence times to the point of release in the distal part of the small intestine are predictable (3-4.5 hours). Suitable tablets of adenosine 5xe2x80x2-triphosphate-disodium salt were prepared containing binders, fillers and stabilizers. The mixtures were granulated and condensed into 250 milligrams of ATP and 500 milligrams of ATP tablets using an oval-shaped punch. The tablets had to provide smooth surfaces, free from edges or sharp curves preferably with concave surfaces, all are properties desirable for the stability and mechanical strength of the enteric coating.
Stabilizers suitable for ATP disodium tablets are magnesium stearate, silica (SiO2)(Sylox), which are suitable stabilizers in small well-established amounts, sodium bicarbonate, ascorbic acid, tocopherols, and maltodextrin, which is especially effective in protecting hygroscopic compositions such as ATP. Suitable fillers for use with ATP in a tablet include microcrystalline cellulose, carboxymethyl cellulose, mannitol or calcium phosphate-dibasic. Binders that are suitable for the ATP therapeutic composition include gum arabic, gelatin, polyvinylpyrrolidone (PVP), hydroxypropylcellulose (HPC) or methylcellulose. A preparation of ATP together with selected stabilizers, fillers and/or binders are then compressed into tablets of optimal size and shape to provide good mechanical strength and surface suitable for enteric coating. Instead of tablets, the blended preparations may be used to form capsules, microtablets or micropellets all of which may, or may not be enteric coated depending on the state of the art.
The function of the pH-dependent enteric coating is to prevent release of the therapeutically active pro-drug-ATP, until it reaches the targeted or desired location of the small intestine such as the distal portion of the small intestine, the section of the ileum where the pH rises to 7.2. The coating thickness is dependent upon the size and shape of the tablets and ranges from 20 to 80 .mu.m. Whereas the traditional enteric polymer coating materials were designed to protect the pharmaceutically active preparation in transit through the stomach, newer coating materials allow for the pH-dependent pills to dissolve only at higher pH""s, with a great degree of accuracy. The older enteric polymer coating materials include cellulose acetate phthalate, polyvinylacetate phthalate, cellulose acetate trimelliate, polyvinyl acetate phthalate and hydroxypropyl methylcellulose phthalate. The preferred materials for enteric coating of ATP therapeutic compositions are methacrylic acid/methyl methacrylate copolymers, which are commercially available from Rhom Pharma under the name Eudragit S and Eudragit L. Eudragit S is a poly(metacrylic acid, methylmetacrylate) 1:2 and Eudragit L is a poly(metacrylic acid, methylmetacrylate) 1:1. Both are anionic copolymers where the ratios refer to the ratios of free carboxyl groups to methyl ester groups. Both copolymers have a mean molecular weight of 135,000. These two copolymers can be mixed in a variety of ratios to achieve a mechanically stable coating of pH sensitivity of between pH""s 6 and 7, with Eudragit S being the preferred ingredient.
After the release of the therapeutic composition of ATP in the small intestine, absorption of adenosine and inorganic phosphate-the catabolic products of ATP, or of ATP itself then follows. Absorption of ATP itself is followed by a rapid degradation to adenosine and inorganic phosphate inside the vascular bed (Slakey et al. 1990; Rapaport and Fontaine 1989; Rapaport and Fontaine 1989b). Both the adenosine and inorganic phosphate are then incorporated into the liver ATP pools (steady state levels), effectively expanding-these pools (Rapaport and Zamecnik 1976; Rapaport and Fontaine 1989). The turnover of the expanded liver ATP pools, ATP pools which supply the adenosine precursor for red blood cell ATP synthesis, then lead to the expansion of red blood cell ATP pools. Expanded red blood cell ATP pools are in turn released from red blood cells into the blood plasma compartment (extracellular) via a non-hemolytic mechanism, where they are rapidly degraded to adenosine and inorganic phosphate (Slakey et al. 1990; Rapaport and Fontaine 1989; Rapaport 1990). The overall established mechanism thus provides for the slow, continuous release of adenosine in the blood plasma after the release of ATP at a preferred position along the distal part of the small intestine.